Method and apparatus for delivering a cased glass stream

ABSTRACT

Apparatus for forming a cased glass stream having an inner core glass surrounded by an outer casing glass that includes a spout for delivering core glass from a first source through a first orifice. A second orifice is vertically spaced beneath and aligned with the first orifice, and is surrounded by an annular chamber that communicates with the second orifice through a gap between the first and second orifices. A tube delivers casing glass from the outlet opening of a casing glass spout to the annular chamber in such a way that glass flows by gravity through the orifices from the first and second sources to form the cased glass stream. A hollow tube within the casing glass spout is positioned with respect to the spout outlet opening for metering flow of casing glass through the outlet opening and delivery tube to the annular chamber surrounding the orifices. The interior of the hollow tube is coupled to a source of gas under pressure so as to maintain the tube interior, and the interior of the thin fall of casing glass through the spout outlet opening, at a pressure above ambient pressure surrounding the casing glass spout. This elevated gas pressure within the casing glass fall reverses the pressure differential between the interior and exterior of the spout outlet opening, so that any tendency for air to migrate through the refractory material surrounding the outlet opening and into the casing glass fall is eliminated.

[0001] This application is a division of application Ser. No. 09/699,539filed Oct. 30, 2000, which is a division of application Ser. No.09/252,400 filed Feb. 18, 1999, now U.S. Pat. No. 6,176,103, which is adivision of application Ser. No. 08/903,785 filed Jul. 21, 1997 and nowabandoned.

[0002] The present invention is directed to delivery of a glass streamfor forming glass charges for glassware manufacture, and moreparticularly to a method and apparatus for delivering a so-called casedglass stream in which an inner or core glass is surrounded by an outeror casing glass.

BACKGROUND AND OBJECTS OF THE INVENTION

[0003] It has heretofore been proposed to provide a cased glass streamfor forming glassware having layered wall segments. U.S. applicationSer. Nos. 08/374,371 and 08/374,372 disclose techniques for deliveringsuch a cased glass stream in which core glass from a first source isdelivered through a first orifice. A second orifice is vertically spacedbeneath and aligned with the first orifice, and is surrounded by anannular chamber that communicates with the second orifice through a gapbetween the first and second orifices. A heated tube delivers casingglass from a second glass source to the annular chamber that surroundsthe second orifice. Glass flows by gravity through the first and secondorifices from the first and second sources in such a way that a casedglass stream emerges from the second orifice. This cased glass streammay be sheared by conventional techniques to form individual cased glassgobs for delivery to conventional individual section glassware formingmachines.

[0004] Although the techniques disclosed in the noted patentapplications address and overcome problems theretofore extant in theart, further improvements remain desirable. For example, the presence ofair bubbles, sometimes termed “blisters,” in the casing glass stream hasbeen a problem. Flow of casing glass from the casing glass spout iscontrolled by a spout tube, which is positioned over the casing glassspout outlet opening so as to meter casing glass flow at the desiredvolumetric ratio relative to core glass flow. However, the volumetricratio of casing glass flow to core glass flow is very low, such as onthe order of 5 to 10%. Consequently, when using conventional glasswareforming equipment, the extremely low volume of casing glass flowingthrough the casing glass spout outlet forms a thin fall, aroundone-quarter inch thick, around the outlet opening and around the upperportion of the heated delivery tube, with the volume within this fallbeing open. After a period of operation, air bubbles or blisters beginto appear in the casing glass stream. It is believed that a chimney-likeeffect of the heated air within the interior of the spout outlet openingand the interior of the casing glass delivery control tube creates apressure differential or gradient between the ambient atmosphere outsideof the casing glass spout and the interior within the thin glass fall.It is believed that this pressure gradient promotes migration of airthrough the refractory material of the casing glass spout, andeventually into the thin glass fall within the spout outlet.

[0005] A number of techniques have been proposed in an effort toeliminate this air bubble or blister problem, including lining of thespout outlet opening with platinum in an effort to block air migration.The technique that is currently preferred is periodically to “flood” thecasing glass outlet and heated delivery tube with casing glass far inexcess of that needed for forming the cased glass stream, and tomaintain this excessive casing glass flow for a period of time. It isbelieved that this “flooding” of the casing glass delivery patheliminates the chimney effect previously described, and further thathydrostatic pressure on the casing glass promotes flow of casing glassinto the refractory material of the spout outlet opening so as to blockair migration paths. When casing glass flow at reduced level is resumed,the air bubbles or blisters are eliminated for a period of time.However, continued use of the ceramic spout requires that the described“flooding” operation be undertaken with increasing frequency, apparentlydue to increasing erosion and wear of the spout material. It is believedthat, as the refractory spout material ages, it becomes more difficultto fill the air migration cracks and passages within casing glass spout.In any event, the described “flooding” operation detracts from glassproduction, and therefore undesirably increases production costs.Furthermore, production of cased glass having air bubbles or blisters inthe casing layer results in undesirably increased scrap rates, furtherincreasing production costs.

[0006] It is therefore a general object of the present invention toprovide a method and apparatus for delivering a glass stream,particularly a cased glass stream, in which formation of air bubbles orblisters in the thin glass fall of the casing glass stream is reduced oreliminated, and in which the need periodically to “flood” the glassstream delivery path is also eliminated. Another and related object ofthe present invention is to provide a method and apparatus fordelivering a glass stream, particularly a cased glass stream, that ischaracterized by improved production efficiency and therefore reducedmanufacturing cost as compared with similar prior art techniques.

SUMMARY OF THE INVENTION

[0007] Apparatus for forming a cased glass stream having an inner coreglass surrounded by an outer casing glass in accordance with a presentlypreferred embodiment of the invention includes a spout for deliveringcore glass from a first source through a first orifice. A second orificeis vertically spaced beneath and aligned with the first orifice, and issurrounded by an annular chamber that communicates with the secondorifice through a gap between the first and second orifices. A tubedelivers casing glass to the annular chamber from the outlet opening ofa casing glass spout in such a way that glass continuously flows bygravity through the orifices from the first and second sources to formthe cased glass stream. A hollow spout tube within the casing glassspout is positioned with respect to the spout outlet opening formetering flow of casing glass through the outlet opening and deliverytube to the annular chamber surrounding the orifices. The interior ofthis spout tube is coupled to a source of gas under pressure so as tomaintain the tube interior and the interior of the thin fall of casingglass through the spout outlet opening at a pressure above ambientpressure surrounding the casing glass spout. This elevated gas pressurewithin the casing glass fall reverses the pressure differential betweenthe interior and exterior of the spout outlet opening, so that anytendency for air to migrate through the refractory material surroundingthe outlet opening and into the casing glass fall is eliminated.

[0008] In accordance with another aspect of the present invention, thereis provided an apparatus for delivering a glass stream that includes aglass spout having a lower outlet opening and a flow control spout tubedisclosed within the spout. The spout tube has a closed upper end, ahollow interior and an open lower end adjacent to the spout outletopening, and position of the tube within the spout is controlled so asto control flow of glass through the outlet opening. The hollow interiorof the flow control tube is coupled to a source of gas under pressure soas to maintain the tube interior at a pressure above that of ambient airsurrounding the spout. Thus, a third aspect of the inventioncontemplates a method of preventing permeation of air through therefractory material around the spout outlet opening into the glassflowing through the outlet opening by delivering gas under pressure tothe flow control tube so as to maintain gas pressure within the tube andwithin the spout outlet opening above ambient air pressure around thespout. By way of example, gas pressure within the flow control tube andthe spout outlet opening may be maintained at a pressure of about twoinches of water column above ambient. The gas maintained under pressurewithin the spout tube may comprise air, nitrogen or argon. In someapplications, such as manufacture of amber glass, it may be desirable toprovide a reducing gas within the spout tube and in contact with theglass flow, which would thus advantageously change the nature of theatmosphere in contact with the glass flow. For example, methane oranother combustible gas may be injected into the spout tube to bum andmaintain a reducing atmosphere at elevated pressure in contact with theglass flow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention, together with additional objects, features andadvantages thereof, will be best understood from the followingdescription, the appended claims and the accompanying drawings in which:

[0010]FIG. 1 is a fragmentary elevational schematic diagram of a glassdelivery system in accordance with a presently preferred embodiment ofthe invention;

[0011]FIG. 2 is a fragmentary sectional view on an enlarged scale of aportion of the delivery system illustrated in FIG. 1;

[0012]FIG. 3 is a fragmentary sectional view on an enlarged scale ofanother portion of the glass delivery system illustrated in FIG. 1; and

[0013]FIG. 4 is a sectional view similar to that of FIG. 3 but showing amodified embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0014] The drawings illustrate a system 10 for delivering a stream ofcased glass. A first forehearth 12 delivers core glass to a bowl orspout 14 that has an opening 16 at the lower end thereof. Spout 14 issurrounded by a protective casing 18, preferably constructed ofnonmagnetic material such as stainless steel. A spout tube 20 and aplunger 22 control delivery of core glass from spout 14 through opening16 to and through one or more first orifices 24 carried by an upperorifice ring 26 beneath spout 14. A lower orifice ring 28 carries one ormore second orifices 30 positioned beneath orifices 24 and axiallyaligned therewith. Orifice(s) 30 is surrounded by an annular chamber 32formed between orifice rings 26, 28. Chamber 32 communicates withorifice(s) 30 by means of a lateral space or gap between orifices 24,30. Annular chamber 32 is coupled by a delivery tube 34 to the opening36 at the lower end of a casing glass spout 38. Spout 38 includes adelivery control spout tube 40, and is coupled to a casing glassforehearth. Delivery tube 34 is, resistance-heated by controlelectronics 41 for maintaining flow of casing glass to chamber 32. Tothe extent thus far described, system 10 is essentially the same asdisclosed in above-noted U.S. application Ser. Nos. 08/374,371 and08/374,372. The former such application is directed in particular toconstruction of casing glass delivery tube 34, while the latter of suchapplications is directed in particular to construction of orifice rings24, 26. The disclosures of such applications, both of which are assignedto the assignee hereof, are incorporated herein by reference forpurposes of background.

[0015] A characteristic of cased glass stream delivery systems is thatthe volumetric ratio of casing glass to core glass is extremely low,which is to say that the quantity of casing glass needed per unit volumeof core glass is extremely low. Consequently, casing glass flow rate isextremely low, and does not fill the volume of either delivery tube 34or spout outlet opening 36. As shown in greater detail in FIG. 2, thelow volumetric flow rate of casing glass is such that the glass thatcontinuously flows beneath the lower open end of spout tube 40 throughspout outlet opening 36 and into the upper end of delivery tube 34 formsa thin wall or fall around the conical interior of opening 36 into theinterior of tube 34. In current systems for commercial production ofcasing glass, this thin layer or fall of casing glass 42 around theinterior of the conical interior of outlet opening 36 is aroundone-quarter inch thick. This thin fall continues into tube 34, which isdisposed at an angle to the axis of opening 36. The glass that initiallytends to flow along the upper surface of tube 34 eventually breaks awayfrom the tube surface, forming a fall 44 that merges into a thin flow 46that flows along the angulated lower surface of tube 34. The flows 42,44, 46 are continuous, smooth and laminar, and do not fold uponthemselves which would tend to trap air bubbles. Consequently, it isbelieved that a “chimney effect,” caused by the heated air within tube40, glass fall 42 and glass falls 44, 46, creates a pressure gradient ordifferential with respect to the external atmosphere, which promotesmigration of air through the refractory material of spout 38 surroundingoutlet opening 36. This air migration eventually reaches the interior ofthe refractory material, and results in bubbles or blisters within fall42.

[0016] To overcome this effect, the present invention contemplates thata source of gas under pressure be coupled to the open interior of spouttube 40, outlet opening 36 and tube 34. Specifically, a cap 50 is placedover the upper end of tube 40. A hollow tube 52 extends upwardly fromcap 40, and is surrounded at its upper end by a tube 54 of largerdiameter. Thus, tubes 52, 54 effectively form a rotary union 56 thatpermits both rotation of tube 40, and vertical motion of tube 40 bymeans of bracket 58 for controlling the flow-metering gap between theopen lower end of tube 40 and the upper end of outlet opening 36. Rotaryunion 56 is coupled by a conduit 59 to a blower 60, which continuouslysupplies gas under pressure (ambient air in this embodiment) throughconduit 59 and union 56 to the hollow interior of tube 40. A gauge 62 iscoupled to union 56 for monitoring air pressure within tube 40. An airdeflector 64 is externally positioned around tube 52 beneath union 56 toprevent direct impingement of air upon cap 50, which would unduly coolthe glass within spout 38.

[0017] The presence of gas under pressure within tube 40 and outletopening 36 splits fall 44 (FIG. 2) and fills the upper interior of tube34 with air. However, because tube 34 is of metal composition,preferably platinum, migration of air through the ceramic insulatingmaterial surrounding tube 34 is not a problem. Rather, it is theelevated air pressure within outlet opening 36 that effectively cancelsthe “chimney effect” formerly extant, and reverses the pressuredifferential or gradient across the ceramic material surrounding thespout outlet. Creation of air bubbles or blisters within the casingglass material is substantially eliminated. It has been found that gaspressure within tube 40 and outlet opening 36 in the range of about 0.05to 10 inches of water column above ambient air pressure, and mostpreferably about two inches of water column above ambient air pressure,yields satisfactory results.

[0018] As noted above, FIGS. 1-3 illustrate a presently preferredembodiment in which the injected gas is air. However, other gases may beemployed for obtaining other desirable effects. FIG. 4 illustrates asystem in which the rotary union 56 a includes a tube 70 for connectingan external gas source 72 to the interior of tube 56. The gas fromsource 72 may comprise nitrogen or argon, for example. In themanufacture of amber glass, for example, it would be desirable tomaintain a reducing or oxygen-lean atmosphere within spout tube 40 incontact with the glass fall to prevent oxidation of the glass. For thispurpose, gas source 72 may comprise a source of methane or othercombustible gas. Combustion of such gas within the upper volume of tube40 will produce the desired reducing atmosphere while maintainingelevated pressure to avoid gas migration through the spout material.

1. Apparatus for delivering a glass stream comprising: a glass spouthaving a lower outlet opening, a spout flow tube disposed within saidspout, said tube having a closed upper end, a hollow interior and anopen lower end disposed adjacent to said spout outlet opening, means forcontrolling position of said tube lower end with respect to said outletopening for controlling glass flow through said outlet opening, and asource of gas at continuous elevated pressure coupled to said interiorvolume of said tube, and through said tube to said opening, continuouslymaintaining said interior volume of said tube at a pressure aboveambient pressure surrounding said spout.
 2. The apparatus set forth inclaim 1 wherein said outlet opening is conical, and wherein said tube ispositioned with respect to said outlet opening so that glass exitingsaid opening forms a film of glass extending around said conicalopening, the interior of said film being pressurized from said tube. 3.The apparatus set forth in claim 2 further comprising a rotary unionconnecting said source to said closed upper end of said tube.